CN112672845A

CN112672845A - Brazing sheet and method for manufacturing same

Info

Publication number: CN112672845A
Application number: CN201980059697.0A
Authority: CN
Inventors: 中村真一; 山吉知树; 土公武宜; 篠田贵弘; 山田诏悟; 园田由彦; 杉本尚规; 本间伸洋; 外山猛敏
Original assignee: Denso Corp; UACJ Corp
Current assignee: UACJ Corp
Priority date: 2018-10-01
Filing date: 2019-09-27
Publication date: 2021-04-16
Anticipated expiration: 2039-09-27
Also published as: US11780034B2; WO2020071289A1; JP2020055013A; JP7165553B2; CN112672845B; US20210394311A1; DE112019004388T5

Abstract

The brazing sheet (1) has: a core material (11) composed of an Al alloy containing 0.20-3.0 mass% of Mg; and a brazing material (12) which is composed of an Al alloy containing Mg, 6.0-13.0 mass% of Si, and more than 0.050 mass% and not more than 1.0 mass% of Bi, is laminated on at least one surface of the core material (11), and is exposed at the outermost surface (121). The brazing material (12) has a boundary surface with the core material (11)(122) The closer to the outermost surface (121), the more continuously decreasing Mg concentration. The depth from the outermost surface (121) is the thickness (t) of the brazing material (12)_f) 1/8 (P)_1/8) The Mg concentration in the region is 0.150 mass% or less, and the depth from the outermost surface (121) is the thickness (t) of the brazing material_f) 7/8 (P)_7/8) The concentration of Mg in the core material (11) is 5-90% of the Mg amount in the core material.

Description

Brazing sheet and method for manufacturing same

Technical Field

The present invention relates to a brazing sheet and a method of manufacturing the same.

Background

For example, aluminum products such as heat exchangers and machine parts have many parts made of aluminum materials (including aluminum and aluminum alloys). These parts are typically brazed from a brazing sheet having a core and a brazing filler metal disposed on at least one side of the core. As a brazing method for an aluminum material, a flux brazing method is often used in which a flux is applied to a surface of a portion to be joined, that is, a portion to be joined by brazing, and is brazed.

However, in the flux brazing method, it is necessary to perform an operation of applying a flux before brazing and an operation of removing the flux or its residue after completion of brazing. These operations result in an increase in the manufacturing cost of the aluminum product. Further, if the flux or its residue cannot be sufficiently removed after the completion of brazing, the surface quality may be deteriorated in the case of performing surface treatment or the like thereafter.

In order to avoid the above-described problems associated with the use of flux, a so-called vacuum brazing method of brazing in vacuum without applying flux to the surface of the joining target portion may be used depending on the application of the aluminum product. However, the vacuum brazing method has a problem that productivity is low or quality of brazed joint is easily deteriorated as compared with the flux brazing method. In addition, the brazing furnace used in the vacuum brazing method has higher equipment cost and maintenance cost than a general brazing furnace.

Therefore, a so-called fluxless brazing method has been proposed in which brazing is performed in an inert gas atmosphere without applying flux to the surface of the part to be joined. The brazing sheet used in the fluxless brazing method has an element in at least one layer of the laminated structure thereof, which has an effect of weakening or breaking the oxide film in the portion to be joined. Mg (magnesium) is often used as such an element.

However, there is a problem that Mg is easily oxidized. Therefore, when Mg is simply added to the brazing filler metal, a coating of MgO may be formed on the surface of the brazing filler metal during brazing heating, and the brazing property may be deteriorated. In order to avoid this problem, the following techniques are proposed: an intermediate material containing Mg is interposed between a core material and a brazing material in a brazing sheet, and Mg is diffused from the intermediate material toward the surface of the brazing material by heating at the time of brazing.

For example, patent document 1 discloses a brazing sheet having: a core material; an intermediate solder layer which is made of an Al-Si-Mg alloy containing 1 mass% or more and less than 4 mass% of Si (silicon) and 0.1 to 5.0 mass% of Mg (magnesium) and which is coated on the core material; an outermost solder layer made of an Al-Si alloy containing 4 to 12 mass% of Si and coated on the intermediate solder layer.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 6055573

Disclosure of Invention

(problems to be solved by the invention)

However, in the case of brazing using the brazing sheet of patent document 1, embrittlement of the oxide film formed of Mg does not occur until the Mg in the intermediate brazing filler metal layer reaches the surface of the brazing sheet. Further, since Mg moves in the solid intermediate solder layer and the outermost solder layer, a long time is required until reaching the surface of the brazing sheet. Therefore, the brazing sheet may cause the above-described brazing defect when the brazing filler metal is thick, when the temperature increase rate is high, or the like.

Further, in the case where an intermediate material is interposed between the core material and the filler metal as in the brazing sheet of patent document 1, the structure of the brazing sheet becomes more complicated because the number of layers included in the brazing sheet is larger than the case where the intermediate material is not provided. In addition, since the number of layers of the brazing sheet is large, productivity may be reduced and material cost may be increased.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a brazing sheet having a simple structure and excellent brazeability in brazing in an inert gas atmosphere, and a method for producing the same.

(means for solving the problems)

An aspect of the present invention is a brazing sheet applicable to brazing performed in an inert gas atmosphere without using a flux, the brazing sheet including:

a core material composed of an aluminum alloy containing 0.20 mass% or more and 3.0 mass% or less of Mg (magnesium):

a brazing material composed of an aluminum alloy containing Mg, 6.0 mass% to 13.0 mass% of Si (silicon), and more than 0.050 mass% to 1.0 mass% of Bi (bismuth), laminated on at least one surface of the core material, and exposed on the outermost surface,

the brazing filler metal has a Mg distribution in which the Mg concentration decreases continuously from the boundary surface with the core material toward the outermost surface,

the Mg concentration at the position 1/8 with the depth from the outermost surface being the thickness of the brazing filler metal is 0.150 mass% or less, and

the Mg concentration at the position 7/8, which is the depth of the brazing filler metal from the outermost surface, is 5-90% of the Mg amount in the core material.

(effect of the invention)

The brazing sheet has the core material and the brazing filler metal laminated on at least one surface of the core material and exposed at the outermost surface. The solder contains Mg and Bi in the specific range. Further, Mg in the filler metal is distributed so that the Mg concentration decreases continuously from the boundary surface with the core material toward the outermost surface of the brazing sheet. The Mg concentration at a position 1/8 where the depth from the outermost surface is the thickness of the solder and the Mg concentration at a position 7/8 where the depth is the thickness of the solder are within the specific ranges.

Bi in the brazing filler metal can suppress the formation of a dense oxide film on the outermost surface of the brazing sheet due to heating during brazing. In addition, Mg in the brazing filler metal can lower the solidus temperature of the brazing filler metal, and produce a molten brazing filler metal from a relatively low temperature. Further, by forming the specific Mg distribution in the filler metal in advance, it is possible to quickly supply Mg to the outermost surface of the brazing sheet while suppressing oxidation of Mg during brazing.

In this way, the formation of an oxide film on the outermost surface of the brazing sheet is suppressed by Bi in the brazing sheet, and Mg is rapidly supplied to the outermost surface, whereby the oxide film existing in the portion to be joined can be broken at an early stage. Further, by generating the molten brazing filler metal from a relatively low temperature, the forming speed of the fillet at the joint scheduled portion can be increased. These effects act synergistically, and thus the solderability in so-called fluxless soldering performed without using flux in an inert gas atmosphere can be improved.

In addition, since the brazing sheet is formed with the specific Mg distribution in a single layer called a filler metal, an increase in the number of layers contained in the brazing sheet can be avoided. Therefore, complication of the structure of the brazing sheet can be avoided, and reduction in productivity or increase in material cost can be avoided.

As a result, according to the above aspect, it is possible to provide a brazing sheet having a good brazeability in brazing in an inert gas atmosphere and a simple structure.

Drawings

Fig. 1 is a partial cross-sectional view showing a main part of a brazing sheet in example 1.

Fig. 2 is a side view of the test piece used for the gap-fill test in example 1.

Fig. 3 is a perspective view of a mini core sample in example 3.

Detailed Description

In the brazing sheet, a brazing filler metal is laminated on at least one surface of a core material. That is, the brazing sheet may have a two-layer structure composed of a core material and a brazing material laminated on one surface of the core material, or may have a three-layer structure composed of a core material and a brazing material laminated on both surfaces of the core material.

The brazing sheet may have a multilayer structure of three or more layers including a core member, a brazing material laminated on one surface of the core member, and a layer made of an aluminum alloy different from the core member and the brazing material and laminated on the other surface of the core member. As the relevant layer, for example, there is a second brazing filler metal having a sacrificial anode material or a chemical composition different from the brazing filler metal, or the like.

When the brazing material is laminated on one surface of the core member and the second brazing material is laminated on the other surface, the second brazing material may not have the specific Mg distribution. In addition, the second filler metal may have a different thickness from the filler metal.

The thickness of the brazing sheet material can be set appropriately from the range of 0.050 to 2.0mm, for example. The coating rate of the brazing filler metal in the brazing sheet can be set as appropriate from a range of 3 to 20%, for example. From the viewpoint of allowing Mg in the filler metal to reach the outermost surface of the brazing sheet at an early stage, the coating rate of the filler metal is preferably 3 to 8%.

The chemical components of each layer constituting the brazing sheet and the reasons for limitations thereof will be described.

(heartwood)

A core material of the brazing sheet is composed of an aluminum alloy containing 0.20 mass% or more and 3.0 mass% or less of Mg. The aluminum alloy constituting the core material may have a chemical composition containing 0.20 mass% or more and 3.0 mass% or less of Mg, for example, and the remainder may be composed of Al (aluminum) and inevitable impurities. The aluminum alloy constituting the core material may contain, as an optional component, Fe (iron), Mn (manganese), Si (silicon), Cu (copper), Zn (zinc), Ti (titanium), and Zr (zirconium) in addition to Mg as an essential component.

Mg: 0.20 to 3.0 mass%

Mg in the core material diffuses by brazing heating at an initial stage of brazing, i.e., at a stage before the brazing filler metal melts, and moves from the core material into the solid brazing filler metal. Therefore, the total amount of Mg in the filler metal gradually increases as the brazing proceeds. After brazing is performed to form a molten brazing material, the oxide film present in the portion to be joined is destroyed by Mg in the molten brazing material. As a result, the brazing sheet and the target material can be brazed without using flux.

By setting the amount of Mg in the core material to 0.20 mass% or more, the total amount of Mg in the molten solder can be sufficiently increased, and the oxide film can be promoted to be broken. As a result, the brazeability between the brazing sheet and the target material can be improved. If the amount of Mg in the core material is less than 0.20 mass%, the total amount of Mg in the molten filler metal is insufficient, and the brazing properties may be deteriorated.

As the Mg content in the core material increases, the oxide film can be more easily broken, and the brazeability can be further improved. From this viewpoint, the content of Mg in the core material is preferably 0.40 mass% or more.

However, if the Mg content in the core material is too large, it is difficult to obtain the effect of improving the brazeability commensurate with the content. In addition, in this case, there is also a possibility that deterioration of formability of the brazing sheet or generation of corrosion due to refinement of crystal grains of the heartwood is caused. By setting the amount of Mg in the core material to 3.0 mass% or less, preferably 1.50 mass% or less, these problems can be avoided and the brazeability between the brazing sheet and the material to be brazed can be improved.

Fe: 1.0 mass% or less

The core material may contain 1.0 mass% or less of Fe as an optional component. Fe has the function of improving the strength of the heartwood. However, if the Fe content is too large, deterioration of the corrosion resistance of the core material may be caused. In addition, in this case, a large precipitate may be easily formed in the core material, and the formability of the brazing sheet may be deteriorated. By setting the Fe content to 1.0 mass% or less, more preferably 0.70 mass% or less, these problems can be avoided and the strength of the core material can be further improved.

Mn: 1.80% by mass or less

The core material may contain Mn of 1.80 mass% or less as an optional component. Mn has the effect of improving the strength of the heartwood. In addition, Mn has the effect of adjusting the potential of the core material and improving corrosion resistance. From the viewpoint of further improving these effects, the Mn content is preferably 0.60 mass% or more. However, if the Mn content is too high, cracks are easily generated in the core material during the manufacturing process of the brazing sheet. By setting the Mn content to 1.80 mass% or less, more preferably 1.30 mass% or less, the strength and corrosion resistance of the core material can be further improved while avoiding deterioration of the manufacturability of the brazing sheet material.

Si: 1.0 mass% or less

The core material may contain 1.0 mass% or less of Si as an optional component. Si has the effect of increasing the strength of the core. However, if the Si content is too large, the melting point of the core material decreases, possibly causing deterioration of brazeability. By setting the Si content to 1.0 mass% or less, the strength of the core material can be further improved while avoiding deterioration of brazeability.

Cu: 1.0 mass% or less

The core material may contain 1.0 mass% or less of Cu as an optional component. Cu has the effect of increasing the strength of the core. In addition, Cu has the effect of adjusting the potential of the core material and improving corrosion resistance. However, if the Cu content is too high, grain boundary corrosion is likely to occur. In this case, the melting point of the core material is lowered, and the brazing property may be deteriorated. By setting the Cu content to 1.0 mass% or less, more preferably 0.50 mass% or less, these problems can be avoided and the strength and corrosion resistance of the core material can be further improved.

Zn: 3.0 mass% or less

The core material may contain 3.0 mass% or less of Zn as an optional component. Zn has the function of reducing the potential of the natural electrode of the heartwood. By lowering the natural potential of the core material, the core material can be made to function as a sacrificial anode. However, if the content of Zn is too large, the natural electrode potential of the core material is excessively lowered, and the sacrificial corrosion preventing effect may be impaired at an early stage. By setting the Zn content to 3.0 mass% or less, more preferably 1.5 mass% or less, the sacrificial corrosion preventing effect achieved by the core material can be maintained for a longer period of time.

Ti: 0.20 mass% or less

The core material may contain 0.20 mass% or less of Ti as an optional component. Ti has an effect of causing corrosion of the core material to progress in a layer shape and suppressing progress of corrosion in the depth direction. However, if the content of Ti is too large, large precipitates are easily formed in the core material, and the rolling property in the production process of the brazing sheet may be deteriorated. In this case, the corrosion resistance of the core material may be deteriorated. By setting the Ti content to 0.20 mass% or less, more preferably 0.15 mass% or less, it is possible to more effectively suppress the progress of corrosion in the depth direction of the core material while avoiding this problem.

Zr: 0.50% by mass or less

The core material may contain 0.50 mass% or less of Zr as an optional component. Zr has the effect of increasing the grain size of the core material and suppressing the occurrence of erosion. However, if the Zr content is too high, cracks are likely to be generated in the core material during the manufacturing process of the brazing sheet. By setting the Zr content to 0.50 mass% or less, more preferably 0.20 mass% or less, it is possible to more effectively suppress the occurrence of corrosion while avoiding deterioration of the manufacturability of the brazing sheet.

(brazing filler metal)

The brazing filler metal for brazing sheet is composed of an aluminum alloy containing Mg, 6.0-13.0 mass% Si, and more than 0.050 mass% Bi and 1.0 mass% Bi. The aluminum alloy constituting the brazing filler metal may have a chemical composition containing Mg, 6.0 mass% to 13.0 mass% of Si, more than 0.050 mass% to 1.0 mass% of Bi, and the balance of Al (aluminum) and inevitable impurities, for example. The aluminum alloy constituting the brazing filler metal may contain Sr (strontium), Sb (antimony), Na (sodium), and Zn (zinc) as optional components in addition to Mg, Bi, and Si as essential components.

Si: 6.0 to 13.0 mass%

Si in the brazing filler metal has the function of lowering the melting point of the brazing filler metal and generating molten brazing filler metal during brazing. By setting the Si content to 6.0 mass% or more, preferably 7.0 mass% or more, a sufficient amount of molten filler metal can be generated at the time of brazing, and brazing between the brazing sheet and the target material can be performed. When the Si content in the brazing filler metal is less than 6.0 mass%, the amount of the molten brazing filler metal is insufficient, possibly causing deterioration in brazeability.

However, if the content of Si in the brazing filler metal is too large, the amount of fusion of the core material during brazing becomes too large, and the strength of the core material after brazing may be reduced. In this case, coarse primary crystal Si is likely to be formed in the brazing material, and molten pores are likely to be generated during heating of brazing. Further, when hot rolling is performed in the manufacturing process of the brazing sheet, the core material may be locally melted due to the presence of primary crystal Si, which may cause the occurrence of rolling cracks. By setting the content of Si in the brazing filler metal to 13.0 mass% or less, preferably 12.0 mass% or less, it is possible to avoid these problems and generate a sufficient amount of molten brazing filler metal.

·Mg

The brazing filler metal contains Mg. The Mg in the brazing filler metal is distributed so that the Mg concentration decreases continuously from the boundary surface with the core material toward the outermost surface. Further, the Mg concentration at a position 1/8 having a depth from the outermost surface of the brazing sheet being the thickness of the filler metal is 0.150 mass% or less, and the Mg concentration at a position 7/8 having a depth from the outermost surface of the brazing sheet being the thickness of the filler metal is 5 to 90% of the Mg amount in the core material.

Here, "continuous" means a state in which the concentration distribution of Mg produced by plotting the Mg concentration at each depth with the vertical axis as the Mg concentration in the brazing material and the horizontal axis as the depth from the outermost surface is in a smooth curve. For example, the brazing filler metal is composed of a plurality of layers having different Mg concentrations, and the Mg concentration distribution is removed from the concept of "continuous" in a stepwise manner.

As described above, Mg present inside the filler metal reaches the outermost surface of the brazing sheet earlier than Mg in the core material by the brazing heating. The oxide film existing in the portion to be joined can be rapidly broken by the Mg. In addition, Mg in the brazing filler metal can lower the solidus temperature of the brazing filler metal, and produce a molten brazing filler metal from a relatively low temperature.

The brazing sheet is capable of sufficiently reducing the amount of Mg present on the outermost surface of the brazing sheet by setting the Mg concentration at a position 1/8 having a depth from the outermost surface that is the thickness of the filler metal to 0.150 mass% or less. This can reduce the amount of MgO produced in the initial stage of brazing, and avoid deterioration of brazeability.

When the Mg concentration at the specific position exceeds 0.150 mass%, Mg is oxidized at the initial stage of brazing, and an MgO film is likely to be formed on the outermost surface of the brazing sheet. Further, the presence of the MgO film may inhibit the oxide film existing in the portion to be joined from being broken, thereby deteriorating the brazeability.

In addition, in the brazing sheet, the concentration of Mg at a position 7/8 having a depth from the outermost surface corresponding to the thickness of the filler metal is set to 5% or more, preferably 20% or more of the amount of Mg in the core material, whereby an appropriate amount of Mg can be quickly brought to the outermost surface of the brazing sheet in the initial stage of brazing. As a result, the oxide film existing in the portion to be joined can be quickly broken. In this case, the solidus temperature of the brazing material can be appropriately lowered, and the fillet forming speed can be increased. As a result, the brazeability can be improved.

When the Mg concentration at the specific position is less than 5% of the Mg amount in the core material, it is difficult to break the oxide film by Mg present in the brazing filler metal. In this case, since the effect of lowering the solidus temperature of the brazing material is low, there is also a possibility that the fillet forming speed is lowered. These results may cause a reduction in brazeability.

From the viewpoint of further improving the brazeability, it is preferable to increase the amount of Mg present in the brazing filler metal. However, if the amount of Mg present inside the filler metal is too large, the amount of Mg reaching the outermost surface of the brazing sheet in the initial stage of brazing is too large. Therefore, an MgO film is easily formed on the outermost surface of the brazing sheet, and the brazeability may be deteriorated. This problem can be avoided by setting the Mg concentration at the specific position to 90% or less, preferably 80% or less, of the Mg amount in the core material.

Bi: more than 0.050% by mass and 1.0% by mass or less

Bi has the effect of inhibiting oxidation of the brazing sheet in brazing. When the Bi content in the brazing filler metal is more than 0.050 mass%, the formation of a dense oxide film due to heating during brazing can be suppressed, and the brazing property can be further improved. Bi is particularly effective when brazing is performed in an inert gas atmosphere having a high oxygen concentration, for example, when the oxygen concentration in the brazing atmosphere is about 50 to 500 ppm by volume. From the viewpoint of further improving the effect of improving the brazeability by Bi, the content of Bi is preferably 0.10 mass% or more.

However, if the content of Bi is too large, it is difficult to obtain the effect of improving the brazeability commensurate with the content of Bi. By setting the Bi content to 1.0 mass% or less, preferably 0.60 mass%, the effect of improving the brazeability commensurate with the Bi content can be obtained.

Sr: 0.10% or less, Sb: 0.10% or less, Na: less than 0.30%

The brazing filler metal may contain one or two or more of 0.10% or less of Sr, 0.10% or less of Sb, and 0.30% or less of Na as optional components. These elements have the effect of refining the structure of the solidified brazing filler metal, which is a joint formed after brazing, and improving the joint strength. From the viewpoint of further improving the effect of improving the bonding strength by these elements, it is preferable that the Sr content is 0.0030 mass% or more, the Sb content is 0.0040 mass% or more, and the Na content is 0.0020 mass% or more.

However, when the contents of Sr, Sb, and Na are too large, it is difficult to obtain the effect of improving the brazeability commensurate with the contents of these elements. By setting the Sr content to 0.10 mass% or less, preferably 0.050 mass% or less, the effect of improving the brazeability commensurate with the Sr content can be obtained. Similarly, by setting the content of Sb to 0.10 mass% or less, preferably 0.050 mass% or less, the effect of improving the brazeability commensurate with the content of Sb can be obtained. Further, by setting the Na content to 0.30 mass% or less, preferably 0.10 mass% or less, the effect of improving the brazeability commensurate with the Na content can be obtained.

Zn: 5.0 mass% or less

The brazing filler metal may contain 5.0 mass% or less of Zn as an optional component. By performing brazing using a brazing material containing Zn, the potential of the brazing material remaining on the surface of the core material after brazing can be reduced. In addition, the corrosion resistance of the brazed aluminum product can be further improved by the sacrificial corrosion prevention effect of the brazing filler metal. From the viewpoint of further improving the effect of improving the corrosion resistance of the aluminum product, the Zn content is more preferably 1.0 mass% or more.

On the other hand, if the Zn content is too high, the potential of the brazing material remaining on the surface of the core material is excessively lowered, and the progress of corrosion may be accelerated. This problem can be avoided by setting the Zn content to 5.0 mass% or less, more preferably 3.0 mass% or less.

(sacrificial Anode Material)

The brazing sheet may have a core material, the brazing filler metal laminated on one surface of the core material, and a brazing filler metal composed of pure aluminum or a mixture containing Zn: a sacrificial anode material which is composed of an aluminum alloy of 8.0 mass% or less and is laminated on the other surface of the core material. In this case, the corrosion resistance of the brazed aluminum product can be further improved by the sacrificial corrosion preventing effect of the sacrificial anode material. The "pure aluminum" refers to an aluminum material having an Al purity of 99.00 mass% or more.

In the case of using an aluminum alloy containing Zn as the sacrificial anode material, the aluminum alloy may also have, for example, a composition containing Zn: more than 0 mass% and not more than 8.0 mass%, and the balance of the chemical components including Al and unavoidable impurities. From the viewpoint of further improving the effect of improving the corrosion resistance of the aluminum product, the Zn content is more preferably 0.50 mass% or more.

On the other hand, if the content of Zn is too large, the potential of the sacrificial anode material is excessively lowered, and the progress of corrosion may become fast. By setting the Zn content to 8.0 mass% or less, more preferably 5.0 mass% or less, this problem can be avoided and the sacrificial corrosion preventing effect can be further improved.

The aluminum alloy constituting the sacrificial anode material may further contain In (indium): 0.0050 to 0.100 mass%, Sn (tin): 0.0050 to 0.100 mass% of one or two kinds. In and Sn have the same effect of lowering the natural electrode potential of the sacrificial anode material as Zn does. However, if the In and Sn contents are too large, the natural electrode potential of the sacrificial anode material is excessively lowered, and the self corrosion resistance may be deteriorated.

By setting the In and Sn contents to 0.0050 mass% or more, more preferably 0.010 mass% or more, the sacrificial anticorrosion effect achieved by the sacrificial anode material can be further improved. Further, by setting the In and Sn contents to 0.100 mass% or less, and more preferably 0.050 mass% or less, respectively, it is possible to obtain a sacrificial anticorrosion effect while avoiding deterioration of self-corrosion resistance.

The sacrificial anode material may further contain 3.0 mass% or less of Mg. Mg in the sacrificial anode material can break an oxide film present on the surface of the sacrificial anode material. Therefore, by using an aluminum alloy containing Mg as the sacrificial anode material, the wettability of the sacrificial anode material with respect to the molten solder can be improved, and the sacrificial anode material and other parts can be brazed together.

However, if the content of Mg in the sacrificial anode material is too large, an oxide of Mg is formed on the surface of the sacrificial anode material, possibly causing deterioration in brazeability. By setting the Mg content in the sacrificial anode material to 3.0 mass% or less, more preferably 1.5 mass% or less, the formation of Mg oxide can be suppressed and the brazeability can be improved.

The sacrificial anode material may further contain one or two or more of 2.0 mass% or less of Mn, 1.5 mass% or less of Si, 1.0 mass% or less of Cu, 0.30 mass% or less of Ti, 0.30 mass% or less of Zr, and 0.30 mass% or less of Cr. These elements have the effect of increasing the strength of the brazing sheet by forming intermetallic compounds in the aluminium matrix phase or by solid solution in the aluminium matrix phase.

(second brazing filler metal)

The brazing sheet may have a core material, the brazing filler metal laminated on one surface of the core material, and a second brazing filler metal composed of an aluminum alloy different from the core material and the brazing filler metal and laminated on the other surface of the core material. A known Al — Si alloy can be used as the aluminum alloy constituting the second brazing material.

The brazing sheet of the above-described aspect can be produced, for example, by the following production method.

First, a clad block is produced, the clad block having a core material block having the chemical components of the core material and a brazing filler metal block made of an aluminum alloy containing 6.0 mass% to 13.0 mass% of Si and more than 0.050 mass% to 1.0 mass% of Bi and overlapping the core material block.

The clad block is hot-rolled to join the layers constituting the clad block, thereby producing a clad material.

Next, the clad material is cold-rolled at one or more passes, and the clad material is heated at least one of between passes of the cold rolling and after the final pass for 1 or more passes to diffuse Mg, thereby forming the Mg distribution in the brazing filler metal.

The clad block can have a laminated structure corresponding to the structure of a desired brazing sheet. For example, when a brazing sheet having a three-layer structure including a core material and the brazing material laminated on both surfaces of the core material is to be produced, a clad block having a three-layer structure may be produced by overlapping a block for the brazing material on both surfaces of a block for the core material.

The hot rolling of the clad block can be performed, for example, under the condition that the rolling start temperature is set to 400 to 500 ℃. In addition, in the hot rolling, the rolling is preferably performed so that the thickness of the clad material is greater than 200% of the thickness of the desired brazing sheet. Since the rolling is performed at a high temperature during the hot rolling, Mg in the core material block diffuses into the brazing material block during the rolling, and an extremely thin Mg diffusion layer is formed in the brazing material of the clad material.

By making the thickness of the clad material larger than 200% of the thickness of the brazing sheet, the Mg diffusion layer can be compressed in the thickness direction in the subsequent cold rolling, and can be made thin enough to be able to ignore the thickness of the Mg diffusion layer. As a result, a desired Mg distribution can be formed with high accuracy in the subsequent heat treatment. When the thickness of the clad material is 200% or less of the thickness of the brazing sheet, the amount of compression of the Mg diffusion layer in the subsequent cold rolling tends to be insufficient. If the compression amount of the Mg diffusion layer is insufficient, it is necessary to diffuse Mg from the core material to the brazing material in consideration of the thickness of the Mg diffusion layer in the subsequent heat treatment. As a result, setting of the heat treatment conditions may become complicated.

After a clad material is produced by hot rolling, the clad material is subjected to cold rolling for one or more passes, and the clad material is heated at least once between passes of the cold rolling and after the final pass to diffuse Mg. That is, when the clad material is subjected to one-pass cold rolling to have a desired thickness, the clad material may be heated after the cold rolling to form the Mg distribution. In the case where the clad material is cold-rolled two or more times to have a desired thickness, the heating may be performed, for example, between any of the passes, or may be performed after the final pass. The heating may be performed at a timing of two or more times between cold rolling passes and after the final pass.

The heating for diffusing Mg may be performed as a heat treatment for adjusting mechanical properties such as intermediate annealing or final annealing, or may be performed as a separate step from these heat treatments.

When diffusing Mg from the core material to the brazing material, it is preferable that D represented by the following numerical formula (1) has a value of 3.0 × 10^-15～3.0×10^-9Under the condition (3), more preferably at 3.0X 10^-11～3.0×10^-9Heating the clad material under the condition of (1).

[ numerical formula 1]

However, n in the above equation (1) is the number of heating times during which the thickness of the clad material is in the range of 100 to 200% of the thickness of the brazing sheet material, and Th_kIs the thickness (m) of the brazing filler metal of the clad material in the kth heating, R is a gas constant (J/mol. multidot.K), t_k0Is the time point when the temperature of the coating material exceeds 50 ℃ in the kth heating, t_k1Is a time point at which the temperature of the coating material is lower than 50 ℃ in the kth heating, and T (t) is the temperature (K) of the coating material at time t. The unit of the small change dt in the above equation (1) is expressed in seconds.

The value of D in the above formula (1) is a value corresponding to the total diffusion distance of Mg, which is heated when the thickness of the covering material is in the range of 100 to 200% of the thickness of the brazing sheet. By setting the value of D within the specific range, Mg can be appropriately diffused into the brazing filler metal, and the specific Mg distribution can be formed more reliably.

In the manufacturing method of the above-described aspect, the surface of the brazing sheet may be etched with an acid as necessary. By performing etching, the oxide scale film formed by heating during hot rolling or heating during diffusion of Mg can be weakened or removed. As a result, the brazeability of the brazing sheet can be further improved.

The etching time is not particularly limited as long as it is a period from the hot rolling to the brazing using the brazing sheet. For example, the hot rolled clad sheet may be etched, or the clad sheet may be etched while it is being cold rolled. Further, etching may be performed after a heat treatment performed after hot rolling until all cold rolling is completed.

The brazing sheet after the heating and the cold rolling are all completed may be etched. After the heating and the cold rolling are all completed, the brazing sheet may be stored in a state having the oxide film, and may be etched before brazing. When the oxide film is weakened or removed at the time of brazing, the brazeability in brazing using the brazing sheet can be improved.

As the acid used for etching of the brazing sheet, an aqueous solution of, for example, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, hydrofluoric acid, or the like can be used. These acids may be used alone or in combination of two or more. From the viewpoint of more efficiently removing the oxide film, a mixed aqueous solution containing hydrofluoric acid and an acid other than hydrofluoric acid is preferably used as the acid, and a mixed aqueous solution of hydrofluoric acid and sulfuric acid or a mixed aqueous solution of hydrofluoric acid and nitric acid is more preferably used.

The etching amount in the etching is preferably 0.05 to 2g/m². By setting the etching amount to 0.05g/m²More preferably 0.1g/m²Thus, the brazing sheet surface can be sufficiently removedThe oxide film on the surface further improves the brazing property.

There is no upper limit on the amount of etching from the viewpoint of improving brazeability of the brazing sheet. However, if the etching amount is too large, it may be difficult to obtain an effect of improving the brazeability commensurate with the processing time. By setting the etching amount to 2g/m²It is more preferably set to 0.5g/m or less²This problem can be avoided as follows.

Examples

Hereinafter, examples of the brazing sheet and the method of manufacturing the same will be described. The brazing sheet and the method for manufacturing the same according to the present invention are not limited to the embodiments of the following examples, and the configuration can be appropriately changed within a range not to impair the gist of the present invention.

The chemical compositions of the core materials used in this example are shown in table 1 (alloy symbols a1 to a 14). The chemical composition of the brazing filler metal used in this example is shown in table 2 (alloy symbols B1 to B10). The symbol "-" in tables 1 and 2 indicates that the element is not positively added and the content does not exceed the content as an inevitable impurity. In addition, the symbol "bal." in this table is a symbol expressed as the remaining part.

[ Table 1]

[ Table 2]

(example 1)

As shown in fig. 1, the present example is an example of a brazing sheet 1 having a two-layer structure including a core material 11 and a brazing filler metal 12 laminated on one surface of the core material 11 (see fig. 1). The brazing sheet 1 of this example is produced as follows. First, a core material block having the chemical composition (alloy symbols a1 to a14) shown in table 1 was produced by continuous casting. Next, the core material block is subjected to planar cutting, and the thickness of the core material block is set to a predetermined thickness.

Separately from the core material blocks, brazing filler metal blocks having chemical compositions (alloy symbols B1 to B10) shown in table 2 were produced by continuous casting. Next, the brazing filler metal block was hot-rolled to set the thickness of the brazing filler metal block to a predetermined thickness.

The core material block and the brazing material block thus obtained were stacked in the combinations shown in tables 3 and 4 to prepare clad blocks. The obtained clad block was hot-rolled, and the core block and the brazing filler metal block were joined to prepare a clad material having a thickness of 3.0 mm.

Next, the clad material was subjected to cold rolling in multiple passes so that the thickness of the clad material became the values shown in tables 3 and 4. After the final pass of the cold rolling, the clad material was heated under heating conditions in which the value of D in the above expression (1) was the values shown in tables 3 and 4. The holding temperature during the heating can be selected from a range of 350 to 450 ℃. The holding time can be selected from the range of 1 to 24 hours, for example. As described above, test pieces C1 to C38 shown in Table 3 and Table 4 were obtained.

Mg distribution in the solder

The Mg distribution in the brazing filler metal 12 in each test piece can be evaluated by the following method. First, each test piece was cut in the sheet width direction, and then the exposed cross section was mirror-polished. In this cross section, as shown in fig. 1, the depth from the outermost surface 111 of the test piece was randomly selected to be the thickness t of the brazing material 12_f1/8, analysis position P_1/8. At each of these analysis positions P_1/8Point analysis by EPMA (i.e., electron probe microanalyzer) was performed to determine each analysis position P_1/8Mg concentration in (c). Moreover, each analysis position P will be analyzed_1/8The average value of the Mg concentration in (1) is defined as the Mg concentration c at the position 1/8 where the depth from the outermost surface 121 is the thickness of the brazing material_1/8. Mg concentration c at the position in each test piece_1/8As shown in tables 3 and 4.

Further, the position where the point analysis by the EPMA was performed was changed to the analysis position P of 7/8 where the depth from the outermost surface 121 of the test piece was the thickness of the solder_7/8Go on and aboveBy the same evaluation, the Mg concentration c at the position 7/8 where the depth from the outermost surface was the thickness of the brazing material was obtained_7/8. Mg concentration c at the position in each test piece_7/8As shown in tables 3 and 4. In tables 3 and 4, the Mg concentration c at the position of each test piece was measured_7/8Its value, the Mg concentration c of the position_7/8Ratio (%) with respect to the amount of Mg in the solder.

Evaluation of solderability by gap filling test

By performing the gap filling test, the brazeability of each test piece can be evaluated. As shown in fig. 2, sample 2 used in the gap filling test has a horizontal plate 21 taken from a test piece and a vertical plate 22 disposed on the brazing material 12 of the horizontal plate 21. The vertical plate 22 is disposed in a direction orthogonal to the horizontal plate 21. Further, one end 221 in the longitudinal direction of the vertical plate 22 abuts against the brazing material 12 of the horizontal plate 21. The horizontal plate 21 of this example has a width of 25mm and a length of 60 mm. The vertical plate 22 is an aluminum plate made of JIS A3003 alloy, and has a width of 25mm, a length of about 55mm, and a thickness of 1 mm.

A spacer 23 is interposed between the other end 222 of the vertical plate 22 in the longitudinal direction and the horizontal plate 21. Thereby, a gap S gradually widening from the one end 221 of the vertical plate 22 toward the spacer 23 side is formed between the horizontal plate 21 and the vertical plate 22. More specifically, the spacer 23 of this example is a round wire made of stainless steel having a diameter of 1.6mm, and is disposed at a position separated by 55mm in the horizontal direction from the position (one end 221) where the vertical plate 22 and the horizontal plate 21 are in contact with each other.

The samples 2 using the test pieces C1 to C29 and the test pieces C33 to C38 were assembled after degreasing the horizontal plate 21 and the vertical plate 22. Further, sample 2 using test pieces C30 to C32 was assembled after degreasing treatment and etching with acid were sequentially performed on the horizontal plate 21 and the vertical plate 22. Thereafter, brazing of sample 2 was performed. Furthermore, no flux was applied to any of the samples prior to brazing.

The brazing of the test specimens was carried out using a nitrogen furnace. The atmosphere in the furnace is a nitrogen atmosphere having an oxygen concentration of 10 ppm by volume or less. The temperature of the sample was raised to 600 ℃, and then the temperature of 600 ℃ was maintained for three minutes to perform brazing heating. After the brazing heating was completed, the sample was slowly cooled in the furnace until the temperature decreased to some extent, and then taken out of the furnace.

In the gap filling test, the brazeability can be evaluated based on the length L and shape (see fig. 2) of the fillet F formed after brazing. In the column of "length of fillet" in tables 3 and 4, as a result of brazing three samples 2, the symbol "a +" is described in the case where the average length L of the gap S filled with the brazing material is 25mm or more, the symbol "a" is described in the case where the average length L is 15mm or more and less than 25mm, and the symbol "B" is described in the case where the average length L is less than 15 mm. In the column of "shape of fillet" in the table, the symbol "a" is described when the fillet is formed uniformly and evenly on both sides of the vertical plate 22, and the symbol "B" is described when the fillet is formed non-uniformly or only on one side of the vertical plate 22.

In the evaluation of brazeability, the case where the length of the fillet is "a +" or "a" and the shape of the fillet is "a" has excellent brazeability, and therefore, it is judged as pass. Further, the case where the length of the fillet is "B" or the shape of the fillet is "B" is inferior in brazeability, and therefore, it is judged as a failure.

[ Table 3]

[ Table 4]

As shown in tables 3 and 4, in the test pieces C1 to C32, the chemical components of the core material 11 and the filler metal 12 were within the specific ranges described above, and an Mg distribution in which the Mg concentration was continuously decreased as the boundary surface 122 (see fig. 1) with the core material 11 was closer to the outermost surface 121 was formed in the filler metal 12. And, at the most distant fromThe depth of the surface 121 is the thickness t of the brazing material 12_f1/8 at the Mg concentration c_1/80.150 mass% or less, and the depth from the outermost surface 121 is the thickness t of the brazing material 12_f7/8 at the Mg concentration c_7/85-90% of Mg in the core material 11. Therefore, these test pieces can improve the brazeability in fluxless brazing.

Of these test pieces, test pieces C30 to C32 were also subjected to etching using an acid. Therefore, the specimens C30 to C32 can improve the brazeability as compared with the specimens C22 to C24 having the same structure except that etching was not performed.

In test piece C33, since the content of Si in the brazing filler metal was less than the specific range, the brazing filler metal generated during brazing was likely to be insufficient. Therefore, in the case of using the test piece C33, the brazing defect is more likely to occur than in the test pieces C1 to C32.

In test piece C34, since the content of Si in the brazing filler metal was larger than the specific range, the core material was easily eroded by the molten brazing filler metal during brazing. Therefore, in the case of using the test piece C34, the core material melted, and brazing might not be possible.

In test piece C35, since the core material contained no Mg, no diffusion of Mg from the core material to the brazing filler metal occurred. Therefore, test piece C35 could not be soldered without flux.

In test piece C36, since the Mg content in the core material was larger than the specific range, the amount of Mg diffused from the core material into the brazing filler metal was likely to be too large. Therefore, in the case of test piece C36, the grains of the core material were refined during brazing, and the occurrence of corrosion was likely to be caused.

In test piece C37, the value of D in the above equation (1) is smaller than the above specific range, and therefore the amount of diffusion of Mg from the core material into the brazing material tends to be insufficient. Therefore, in the case of using the test piece C37, the brazing defect is more likely to occur than in the test pieces C1 to C32.

In test piece C38, since the value of D in the above equation (1) is larger than the above specific range, the amount of Mg reaching the surface of the brazing filler metal tends to be too large. Therefore, when test piece C38 was used, a dense film of MgO was formed on the outermost surface of the test piece during brazing, and this may cause deterioration in brazeability.

(example 2)

This example is an example of a brazing sheet having a thickness of 1.0 mm. The test pieces D1 to D4 of the present example shown in table 5 were produced in the same manner as the test pieces C1 to C38 in example 1, except that the thickness was changed to 1.0 mm.

For sample 2 using test pieces D1 to D3, sample 2 was assembled after degreasing horizontal plate 21 and vertical plate 22. In addition, sample 2 using test piece D4 was assembled after degreasing and etching with acid were sequentially performed on horizontal plate 21 and vertical plate 22. Thereafter, brazing of sample 2 was performed under the same conditions as in example 1. In addition, no flux was applied to any of samples 2 prior to brazing. Table 5 shows the results of evaluating the Mg distribution and brazeability of the test pieces D1 to D4 by the same method as in example 1.

In the column of "length of fillet" in table 5, as a result of brazing three samples 2, the symbol "a +" is described in the case where the average length of the gap S filled with the brazing material is 30mm or more, the symbol "a" is described in the case where the average length is 20mm or more and less than 30mm, and the symbol "B" is described in the case where the average length is less than 20 mm. In the column of "shape of fillet" in the table, the symbol "a" is described when the fillet is formed uniformly and evenly on both sides of the vertical plate 22, and the symbol "B" is described when the fillet is formed non-uniformly or only on one side of the vertical plate 22.

[ Table 5]

As shown in table 5, in the test pieces D1 to D4, the chemical components of the core material and the brazing filler metal were within the specific ranges, and the specific Mg distribution was formed inside the brazing filler metal. Therefore, these test pieces can improve the brazeability in fluxless brazing. Further, as can be understood from comparison of test piece D1 and test piece D4 in which the core material and the brazing filler metal have the same chemical composition, the length of the fillet is increased by etching using an acid, and the brazeability is further improved.

(example 3)

This example is an example of a brazing sheet having a three-layer structure in which a brazing material is laminated on both surfaces of a core material. Test pieces E1 to E6 of the present example shown in table 6 were produced by stacking both surfaces of a brazing material block and a core material block, and then sequentially performing hot rolling, cold rolling, and heating in the same manner as in example 1. The thickness of the test pieces E1 to E6 in this example was 0.050 mm.

In this example, the brazing property was evaluated using a mini-core sample 3 simulating the core of the corrugated fin type heat exchanger. As shown in fig. 3, the mini core sample 3 includes a corrugated fin 31 made of a test piece, and two flat plates 32 sandwiching the corrugated fin 31. The corrugated fin 31 of this example has a length of 50mm and a height of 10mm, and the adjacent crests 311 are spaced apart by 3 mm. The flat plate 32 of this example is an aluminum plate made of JIS A3003 alloy, and has a length of 60mm, a width of 16mm and a thickness of 0.50 mm.

The mini core samples 3 using the test pieces E1 to E4 and the test piece E6 were assembled after degreasing the corrugated fin 31 and the flat plate 32. In the mini core sample 3 using the test specimen E5, the corrugated fin 31 and the flat plate 32 were degreased, and then the corrugated fin 31 was etched with acid. Then, the mini core sample 3 is assembled using the corrugated fin 31 and the flat plate 32. The mini core sample 3 was assembled and then brazed under the same conditions as in example 1. Furthermore, no flux was applied to any mini-core sample 3 prior to brazing.

The method for evaluating the brazeability of the mini core sample 3 is as follows. First, the corrugated fin 31 is cut out from the mini core sample 3 after brazing. Then, the length of the corner-filling trace existing on each flat plate 32 in the width direction of the flat plate 32 is measured, and the total of these is calculated. Separately from this, the total of the lengths in the plate width direction of the fillet when the flat plate 32 and the corrugated fin 31 are assumed to be completely joined is calculated. The ratio of the former value to the latter value was defined as the bonding ratio (%) of the corrugated fin 31 in each sample 3. The latter value can be calculated by multiplying the width of the corrugated fin 31 and the number of crests 311 of the corrugated fin 31, for example.

In the column of "brazeability" in table 6, as a result of brazing three mini-core samples 3, the symbol "a" is described when the average of the joint ratios is 80% or more, and the symbol "B" is described when the average of the joint ratios is less than 80%. In the evaluation of the brazeability of this example, the average of the joint ratios of 80% or more was excellent in brazeability, and therefore, it was judged as being acceptable. In addition, since the average of the joining ratio is less than 80%, the brazeability is poor, and therefore, it is determined as a failure.

[ Table 6]

As shown in table 6, in test pieces E1 to E5, the chemical components of the core material and the brazing filler metal were within the specific ranges, and the specific Mg distribution was formed inside the brazing filler metal. Therefore, these test pieces can improve the brazeability in fluxless brazing. Of these test pieces, test piece E5 was also subjected to etching using an acid. Therefore, the brazing property of test piece E5 was improved as compared with test piece E2 having the same structure except that etching was not performed.

On the other hand, in test specimen E6, since the value of D in the above numerical expression (1) was smaller than the above specific range, the amount of diffusion of Mg from the core material into the brazing material was likely to be insufficient. Therefore, in the case of using the test piece E6, poor brazing is more likely to occur than the test pieces E1 to E5.

As can be understood from the results of examples 1 to 3 described above, by setting the chemical components of the core material and the filler metal within the specific ranges and forming the specific Mg distribution in the filler metal, a brazing sheet excellent in brazeability in fluxless brazing can be obtained.

Claims

1. A brazing sheet applicable to brazing performed in an inert gas atmosphere without using a flux, comprising:

a core material composed of an aluminum alloy containing 0.20 mass% or more and 3.0 mass% or less of Mg;

a brazing material composed of an aluminum alloy containing Mg, 6.0 to 13.0 mass% of Si, and more than 0.050 to 1.0 mass% of Bi, the brazing material being laminated on at least one surface of the core material and being exposed at the outermost surface,

2. The brazing sheet according to claim 1,

the brazing filler metal further contains one or two or more of 0.10 mass% or less of Sr, 0.10 mass% or less of Sb, and 0.30 mass% or less of Na.

3. The brazing sheet according to claim 1 or 2,

the brazing filler metal further contains 5.0 mass% or less of Zn.

4. The brazing sheet according to any one of claims 1 to 3,

the core material further contains one or two or more of 1.0 mass% or less of Fe, 1.80 mass% or less of Mn, 1.0 mass% or less of Si, 1.0 mass% or less of Cu, 3.0 mass% or less of Zn, 0.20 mass% or less of Ti, and 0.50 mass% or less of Zr.

5. The brazing sheet according to any one of claims 1 to 4,

the brazing filler metal is laminated on both surfaces of the core material.

6. The brazing sheet according to any one of claims 1 to 4,

the brazing sheet comprises the core material, the brazing filler metal laminated on one surface of the core material, and a sacrificial anode material composed of pure aluminum or an aluminum alloy containing 8.0 mass% or less of Zn and laminated on the other surface of the core material.

7. The brazing sheet according to claim 6,

the sacrificial anode material is further composed of an aluminum alloy containing one or more of 2.0 mass% or less of Mn, 3.0 mass% or less of Mg, 1.5 mass% or less of Si, 1.0 mass% or less of Fe, 1.0 mass% or less of Cu, 0.3 mass% or less of Ti, 0.3 mass% or less of Zr, and 0.3 mass% or less of Cr.

8. The brazing sheet according to claim 6 or 7,

the sacrificial anode material further comprises an aluminum alloy containing one or more of 0.0050 to 0.100 mass% of In and 0.0050 to 0.100 mass% of Sn.

9. A method of manufacturing a brazing sheet material, the brazing sheet material according to any one of claims 1 to 8 being manufactured,

producing a clad block having a core material block having a chemical component of the core material and a brazing filler metal block made of an aluminum alloy containing 6.0 mass% to 13.0 mass% of Si and more than 0.050 mass% to 1.0 mass% of Bi and overlapping the core material block,

hot rolling the clad block to join the layers constituting the clad block to produce a clad material,

the clad material is cold-rolled at one or more passes, and the clad material is heated at least one time between passes of the cold rolling and after the final pass to diffuse Mg, thereby forming the Mg distribution in the brazing filler metal.

10. The method of manufacturing a brazing sheet according to claim 9,

when Mg is diffused from the core material to the brazing material, the value of D represented by the following numerical formula (1) is 3.0X 10^-15～3.0×10^-9Under conditions such that the clad material is heated,

wherein n in the formula (1) is the number of heating times during which the thickness of the clad material is in the range of 100 to 200% of the thickness of the brazing sheet material, Th_kIs the thickness of the brazing filler metal of the clad material in the kth heating in m, R is a gas constant in J/mol. multidot.K, t_k0Is the time point when the temperature of the coating material exceeds 50 ℃ in the kth heating, t_k1Is the time at which the temperature of the coating material in the kth heating is below 50 ℃, and t (t) is the temperature of the coating material at time t, in K.

11. The method of manufacturing a brazing sheet according to claim 9 or 10,

after the hot rolling, the surface of the clad material is etched with an acid until brazing with the brazing sheet.

12. The method of manufacturing a brazing sheet according to claim 11,

the etching amount in the etching is 0.05-2 g/m²。